UNIT V: lesson 6
Molar Concentration & Dilutions
CONCENTRATION
Concentration of a substance in a solution is the
amount of this substance that exists in in a volume
of solution.
A concentrated solution: has a relatively high
concentration (There is a large amount of the
substance dissolved in the solution)
A dilute solution: has a relatively low
concentration ( very little substance is dissolved
in the solution).
MOLAR CONCENTRATIONS
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Chemists like to use ‘mole’ to describe amount of
substance in solutions.
Molar Concentration or Molarity (M) is the
number of moles (n) of the substance in 1 L of
solution.

Units for Molarity
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A short hand symbol for Molar Concentration is
MOLAR CONCENTRATION
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
Ex: what is the molar concentration of 1 L of
solution containing 2.5 mol of NaCl?
Ex: what is the [NaCl] in a solution containing
5.12 g of NaCl in 250 mL of solution?

What mass of NaOH is contained in 4 L of 0.2 M
NaOH?
What is the molariy of H2SO4 having a density of
1.839 g/mL?
DILUTION CALCULATIONS

What happens when you mix two solutions
together?!
Mixing two solutions together will dilute the original
solutions.
 This means, there will be new concentrations and
new volumes

DILUTION CALCULATIONS
Molarity/Concentration = moles(n)
Volume (L)
Molarity of Mixture = Total moles (n)
Total volume of mixture (L)
DILUTION CALCULATIONS
*Consider a concentrated solution that we add water to
in order to make a diluted solution.
 CI = initial concentration of solution
 VI= initial volume of solution
After we add water….
CDIL = diluted concentration (after water is
added)
 VDIL = (total) diluted volume (after water is
added)
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DILUTION CALCULATIONS
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Recall that c = n/V...
therefore n= c·V
nI = moles for Initial solutions
= CI x VI
nDIL = moles in DIL solution
= CDIL x VDIL
The Total number of moles (n) for each solution
that we started with does not change when we
mix the two solutions together….it stays the
same.
DILUTION CALCULATIONS
nI = nDIL
CI x VI = CDIL x VDIL
or...
CIVI = CFVF
A. Simple Dilution of a Chemical in Solution
Example #1: If 400.0 mL of 0.800M HCl is added
to 500.0 mL of water, what is the resulting [HCl]
in the mixture?
B. Mixing 2 Solutions with Different
Concentrations
 Treat mixtures of two solutions as two
separate “single dilutions”
Example #2: If 300.0 mL of 0.350 M H2SO4 is
added to 400.0 mL of 0.050 M H2SO4, what is the
resulting [H2SO4] in the mixture?
C. Making a Dilute Solution from a
Concentrated Solution
Example #3: What volume of 8.00 M H2O2 is used
in making up 1.5 L of 0.5 M H2O2?
TRY:
Miss Q. mixes 200mL of water with 50 mL of a
sodium chloride solution having an unknown
concentration. Miss Q. finds that the molarity of
the sodium chloride after dilution was 0.0864 M.
What was the molarity of the original sodium chloride
solution??
SUMMARY OF DILUTION CALCULATIONS
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Always, always, always use
Remember for final volume (VF) to add up the
two volumes together. It is a total volume.
Be careful when you are substituting the
numbers in the equation.
SUMMARY OF DILUTION CALCULATIONS
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Always, always, always use
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To find new concentration, simply rearrange into
[New concentration] = [old concentration] x old volume
total volume
REMEMBER…
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Molarity is the same as molar concentration.
It is in moles/L
 If you have units in moles/mL, must change it
into moles/L first.

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Ex: 500 mL L
Divide by 1000
 = 0.5 L

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If you have units in grams, change g moles by
using the molar mass!
TRY
Suppose you have 5.60g of KCl and you wanted to
make a 2.14 M solution. What volume of solution
would you create?
HOMEWORK
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Page102
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#78, 80, 81, 83, 84, 85,87, 90